From: Alexander Zarochentsev <alexander_zarochentsev@xyratex.com>
Date: Wed, 23 Jul 2014 20:10:24 +0000 (-0700)
Subject: LU-5397 obdclass: optimize busy loop wait
X-Git-Tag: 2.6.51~77
X-Git-Url: https://git.whamcloud.com/?p=fs%2Flustre-release.git;a=commitdiff_plain;h=7887a397220d84db8b38c6fc4892c3f5c5f3ad01

LU-5397 obdclass: optimize busy loop wait

two optimizations in the busy loop wait in class_cleanup():
(1) remove unnecessary spinlocks protecting obd_conn_inprogress
    access
(2) replace cond_resched by more suitable yield to unconditionally
    yield the CPU if the condition check fails.

Xyratex-bug-id: MRP-1991
Signed-off-by: Alexander Zarochentsev <alexander_zarochentsev@xyratex.com>
Change-Id: I9079b2d04afda7d6db902392c6dcb216706a7ae4
Reviewed-on: http://review.whamcloud.com/11198
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Tested-by: Jenkins
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
---

diff --git a/lustre/obdclass/obd_config.c b/lustre/obdclass/obd_config.c
index 645e5aa..3914193 100644
--- a/lustre/obdclass/obd_config.c
+++ b/lustre/obdclass/obd_config.c
@@ -624,16 +624,12 @@ int class_cleanup(struct obd_device *obd, struct lustre_cfg *lcfg)
 	}
 	/* Leave this on forever */
 	obd->obd_stopping = 1;
+	spin_unlock(&obd->obd_dev_lock);
 
 	/* wait for already-arrived-connections to finish. */
-	while (obd->obd_conn_inprogress > 0) {
-		spin_unlock(&obd->obd_dev_lock);
-
-		cond_resched();
-
-		spin_lock(&obd->obd_dev_lock);
-	}
-	spin_unlock(&obd->obd_dev_lock);
+	while (obd->obd_conn_inprogress > 0)
+		yield();
+	smp_rmb();
 
         if (lcfg->lcfg_bufcount >= 2 && LUSTRE_CFG_BUFLEN(lcfg, 1) > 0) {
                 for (flag = lustre_cfg_string(lcfg, 1); *flag != 0; flag++)